The process of blood vessel repair following injury is carried out in a temporal and spatial manner by the dynamic interaction of fibrinogen (FBG), fibrin and the extracellular matrix (ECM) with cells of the vessel walls. The long term objectives of this proposal are to characterize the cellular and molecular mechanisms by which vessel repair occurs. Proteoglycans are essential components of the receptor- growth factor interactions, cell-cell recognition systems, and cell-ECM adhesion processes that interact coordinately to stimulate cell proliferation and migration required for cellular repair. Because cell surface heparan sulfate proteoglycans perform essential functions in these processes, and with the extensive clinical application of heparin in the prevention in the prevention of thrombosis, the potential for heparin binding to fibrin(ogen) has important implications in understanding the mechanisms of heparin modulation of hemostasis, fibrinolysis, angiogenesis and tissue remodeling. Preliminary studies demonstrate that FBG, not fibrin, is incorporated into ECM, resulting in exposure of a cryptic heparin binding domain (HBD). We will test the hypothesis that FBG, through its HBD, plays an active role in heparin and heparin sulfate modulation of cell-cell and cell-matrix interactions involved in vessel repair. The proposed experiments will elucidate the mechanisms by which FBG is assembled into preformed, mature matrices of polarized and interstitial cell types to determine the functional role of matrix-FBG in mediating signal transduction to bring about the ordered process of cell repair and tissue remodeling. Specific Aim 1 of this proposal will be to define the essential structural domains of matrix FBG, and to determine the reciprocal cell-surface receptors and matrix constituents that support assembly of FBG into ECM. The techniques of cell biology, protein biochemistry, confocal scanning laser cytometry, fluorescence microscopy, and immunodetection will be used to characterize the ligands and receptors critical for the assembly of FBG into ECM. Specific Aim 2 will be to examine the cellular responses to FBG deposited and assembled into mature ECM. Modulation of cell proliferation and migration by FBG deposited into ECM, including the signal transduction pathways involved, will be examined using cell and molecular biology techniques. Defining the structure/function relationships involved in FBG, fibrin and the ECM interaction with cells of the vessel wall will provide a new understanding of the host response to injury with implications for treatment of thrombosis and therapeutic manipulation of angiogenesis.